I downloaded it from the SF page, where I stumbled upon it. (I can see you haven't announced the OS X build yet, so I'm a bit hesitant to report these, but here goes anyways. Hope it's ok.)
SDL_ttf appears to be missing from the .app bundle and the game doesn't start. The icon flashes briefly in the dock and then disappears.
A quick glance in console.log, showed the following.
It looks for SDL_ttf in @executable_path/../Frameworks/SDL_ttf.framework but doesn't find it - because it's not there.
I downloaded SDL_ttf from the SDL website and copied SDL_ttf.framework into the .app-bundle (Contents/Frameworks) and that seemed to work.
Then another problem appeared...
When I tried to start the game, it still wouldn't do anything but flash the icon briefly in the dock. Back to console.log, where I found this:
===== From console.log =====
---> Fixing Working Directory, depending on Finder Call !
Path Length : 46
Changing wd to path /Applications/games/Ufo.app/Contents/MacOS/ufo
/Applications/games/Ufo.app/Contents/MacOS/¯ = neuer Pfad
Adding game dir: ./base
using /Users/madsen/.ufoai/2.1.1/base for writing
Adding game dir: /Users/madsen/.ufoai/2.1.1/base
couldn't exec default.cfg
couldn't exec config.cfg
couldn't exec keys.cfg
Hostname: macsvin.local
IP: 10.0.0.6
...using language: C
Console initialized.
------- sound initialization -------
Loading snd_sdl sound driver
...library search path: '.'
Load library failed: dlopen(./snd_sdl.so, 1): image not found
------- Loading ref_sdl.dylib -------
LoadLibrary ("./ref_sdl.dylib") failed: No such file or directory
Dumped console text to /Users/madsen/.ufoai/2.1.1/base/gl_debug.txt.
recursive shutdown
Error: Couldn't initialize OpenGL renderer!
Consult gl_debug.txt for further information.
===== End =====
I'm not really sure how to deal with that, so I'm giving up for tonight, but maybe you can make something of it.
Best,
---Madsen